Modelling Interfacial Package Creep in High Temperature Electronics
Interfacial package creep modeling requires viscoplastic constitutive equations and temperature-dependent stress mapping to prevent long-term field drift.
Viscoplasticity Modeling
Computational Framework
Mathematical representation of material behavior combines the effects of rate dependent plasticity and viscous flow. Structural engineers employ viscoplasticity modeling to simulate the response of metals and polymers to high temperature loading and rapid deformation. This approach links the stress to the strain rate, allowing for the prediction of creep and stress relaxation.
The equations describe how the yield surface evolves with time and temperature.
Constitutive Law
Unified constitutive laws provide a method for calculating the inelastic strain in solder alloys without a separate yield criterion. Within the context of viscoplasticity modeling, the Anand model uses a specific set of material parameters to describe the deformation resistance and hardening behavior. These constants are derived from experimental data gathered during constant strain rate and constant stress tests.
The model is widely implemented in commercial finite element software for reliability analysis. This framework allows for the calculation of the accumulated plastic work which is a primary indicator of fatigue damage in lead free solder.
Parameter Extraction
Curve fitting algorithms match the simulated response to the results of physical tensile and creep experiments. Technicians verify viscoplasticity modeling parameters by testing the material across a range of temperatures and loading speeds. Errors in the parameter set can lead to large discrepancies between the predicted and actual life of the component.
Precise control of the test environment is necessary to obtain high quality calibration data.
Simulation Output
Results from the analysis show the distribution of plastic work and the evolution of the stress state over the service life. Designers use viscoplasticity modeling to optimize the geometry of interconnects and reduce the risk of thermal fatigue. The simulation stops being accurate if the material undergoes a phase change or extensive microstructural damage not captured by the equations.